I. Field
The present disclosure relates generally to communication, and more specifically to techniques for transmitting data in a multiple-input multiple-output (MIMO) system.
II. Background
In a wireless communication system, a transmitter (e.g., a base station or a terminal) may utilize multiple (T) transmit antennas for data transmission to a receiver equipped with multiple (R) receive antennas. The multiple transmit and receive antennas form a MIMO channel that may be used to increase throughput and/or improve reliability. For example, the transmitter may transmit T data streams simultaneously from the T transmit antennas to improve throughput. Alternatively, the transmitter may transmit a single data stream redundantly from all T transmit antennas to improve reception by the receiver.
The transmission from each transmit antenna causes interference to the transmissions from the other transmit antennas. In some instances, improved performance may be achieved by transmitting fewer than T data streams simultaneously from the T transmit antennas. For example, a subset of the T transmit antennas may be selected, and a data stream may be sent from each selected transmit antenna. The transmit antenna(s) that are not used for transmission do not cause interference to the transmit antenna(s) that are used for transmission. Hence, improved performance may be achieved for the data stream(s) sent on the selected transmit antenna(s).
Rank prediction refers to the determination of the rank of a MIMO channel or, equivalently, the number of data streams that can be transmitted simultaneously via the MIMO channel. If too many data streams are sent, then excessive interference may be observed by each of these data streams and the overall performance may suffer. Conversely, if too few data streams are sent, then the capacity of the MIMO channel is not fully utilized.
There is therefore a need in the art for techniques to determine the rank of a MIMO channel.